Biomedical Engineering Reference
In-Depth Information
consolidation, most notably problems in rock mechanics. Certain porous rocks,
marbles, and granites have material properties that are similar to those of bones
[7].
The structure of this chapter is first to describe the vascular system in a bone
and then describe the interstitial fluid movement in the bone as well as the
factors that drive these flows and cause changes in the flow patterns associated
with diseases, surgery, and whole body movement. Thus, the sections that follow
immediately describe the arterial system, the microvascular network of marrow,
the microvascular network of cortical bone, and the venous drainage of bone. The
connections between the vascular system and the interstitial fluid system are then
described in Section 9.6 on bone lymphatics and blood vessel trans-vessel-wall
transport. Attention then turns to the spaces in bone tissue occupied by these
two fluid systems, the vascular porosity (PV) and the lacunar-canalicular porosity
(PLC), and the interfaces between the systems. The remainder of the chapter
considers different aspects of interstitial fluid flow.
9.2
Arterial Supply
9.2.1
Overview of the Arterial System in Bone
All elements of a bone, including the marrow, perichondrium, epiphysis, meta-
physes, and diaphyses, are richly supplied by vasculature. Mature long bones in all
species have three sources of blood supply: (i) the multiple metaphyseal-epiphyseal
vessel complex at the ends of the bones, (ii) the ''nutrient'' artery entering the
diaphyses (Figure 9.1), and (iii) the periosteal vessels (Figures 9.1 and 9.2). After
entering the diaphyses, the nutrient artery divides into ascending and descending
branches, which have further, radially orientated, branches streaming to the bone
cortex (Figure 9.1). Usually a single nutrient artery enters the diaphyses of a long
bone, though many human long bones such as the femur, tibia, and humerus
often have two. When the nutrient artery enters a bone, the vessel has a thick
wall consisting of several cell layers, but within the medulla it rapidly becomes a
thin-walled vessel with two cell layers and minimal supporting connective tissue
[8]. After reaching the medullary cavity the nutrient artery divides into ascend-
ing and descending branches, which proceed toward the metaphyseal bony ends
(Figure 9.1). These branches approach the epiphyseal ends of the bone, subdivid-
ing repeatedly along the way into branches, which pursue a helical course in the
juxta-endosteal medullary bone. The terminal branches of the main ascending and
descending branches supply the ends of the long bone and anastomose freely with
the metaphyseal vessels. The vessels divide and subdivide to feed into a complex
network of sinusoids (Figures 9.1 and 9.3). In the immature bone, the open carti-
laginous epiphyseal growth plate separates the epiphyseal and metaphyseal vessel
complexes.
